If you're anything like us, you have days where you obsessively check your weight, hoping the number on the scale will drop at least half a pound (unfortunately, those days tend to become more and more frequent in the middle of bikini season).

But before you get all bummed out about your "number," you should know the facts (and myths) about what affects your weight.

We asked Karen Ansel, registered dietitian in New York and spokeswoman for the American Dietetic Association, to give us the skinny on our five most pressing weight questions:

1. Is it true that we weigh less in the morning?

Generally, yes, because you don't have the added weight of a recent undigested meal. During the day, when you're eating and drinking, those foods (and fluids) add weight—at least until they're digested and excreted. Just a cup of water adds half a pound, for example—and 20 percent of most meals are water, which adds up to a lot of extra weight. Since you're not eating or drinking during the night (unless you get the midnight munchies), your body has a chance to remove extra fluids (that's why you pee so much in the morning when you wake up). So weigh yourself in the morning ... after you pee.

2. After we go No. 2?

Yes—for obvious reasons! But for those of you who aren't squeamish, we'll explain. When you have a bowel movement, you're emptying your colon. Depending how much you go, that visit to the ladies' room can add up to half a pound a day—hence the reason you feel so much lighter after you poop. If you're the type of person who takes care of business first thing in the morning, weigh yourself right after you go. If you're more likely to go after breakfast, weigh yourself first so your meal doesn't add extra pounds to the scale. Either way works as long as you're consistent.

3. Do we really weigh more when we're soaking wet?

Probably not. Any water on your body, or in your hair, probably wouldn't account for more than an ounce or two (1/16th or 1/8th of a pound).

4. Does it matter if you have clothing/undies on? Or should you be totally nude?

Not really. The trick is to stay consistent from one day to the next, so you can adequately measure real change. So don't weigh yourself in your birthday suit one day and wearing sweats and tennis shoes the next. If you do choose to weigh yourself fully clothed, you can deduct anywhere from a half a pound to two pounds (depending what you're wearing) to get your "real" weight.

5. We know that muscle weighs more than fat. So does that mean if we buff up for summer, we'll weigh more?

Muscle does weigh more than fat, so if you gain muscle without losing fat, you'll end up weighing more. Ideally, you want to gain muscle while losing fat, so the number on the scale shouldn't change that much if you're truly improving your fitness and body composition.

A little side note: If the number on the scale affects the quality of your day, it's time to ditch your scale. Still can't rid yourself of your daily weigh-in? Focus on staying between a 5-pound-range (plus or minus)—not an exact weight. If your weight fluctuates a couple of pounds, it might just be because you're in between bowel movements, or you had a salty meal.